Respiration is the process by which animals inhale and exhale oxygen. In this process, oxygen and carbon dioxide are typically exchanged in the lungs. This process is important for most land animals, as respiration is typically involved in the only process by which animals incorporate oxygen, an essential molecule for the proper functioning of the body.
With reference to FIG. 1, the human heart is composed of four chambers; the right and left atria and the right and left ventricles. Each chamber of the heart has a valve at its exit such that blood passing through the valve is largely prevented from going back in to that chamber. The Superior Vena Cava 1 collects blood from the upper half of the body. The Inferior Vena Cava 2 collects blood from the lower half of the body. Blood leaves the Superior Vena Cava 1 and the Inferior Vena Cava 2 and enters the Right Atrium 3. Blood entering the Right Atrium 3 is generally deoxygenated blood. When the Right Atrium 3 contracts, the blood goes through the Tricuspid Valve 4 and into the Right Ventricle 5. When the Right Ventricle 5 contracts blood is pumped through the Pulmonary Valve 6, into the Pulmonary Artery 7 and then to the lungs where it picks up oxygen.
Blood returns to the heart from the lungs by way of the Pulmonary Veins 8 and goes into the Left Atrium 9. When the Left Atrium 9 contracts, blood travels through the Mitral Valve 10 and into the Left Ventricle 11. The Left Ventricle 11 is the chamber that pumps blood through the Aortic Valve 12 and into the Aorta 13 to the rest of the body. The Aorta is the main artery of the body, and receives all the blood that the heart has pumped out and distributes it to the rest of the body. The Left Ventricle 11 typically has a thicker muscle than any other heart chamber because it must pump blood to the rest of the body against much higher pressure in the general circulation (blood pressure).
The Left and Right Atria generally contract at about the same time. Also, the Left and Right Ventricles generally contract at about the same time. This generally leads to a nearly synchronous opening and closing of the Tricuspid Valve 4 and the Mitral Valve 10, and a nearly synchronous opening and closing of the Pulmonary Valve 6 and Aortic Valve 12. When the valves close, they tend to make generally lower frequency sounds. These sounds generally contribute to the “thump, thump” sound typically associated with the heart; the closing of the atrial valves being the first “thump”, and the closing of the ventriclular valves being the second “thump”. Since the atria-closing valves generally occur at about the same time and since the ventricle-closing valves generally occur about the same time, the closing of the four valves generally only leads to two sounds. These sounds are classified as the S1 (the atria-closing sound) and the S2 (the ventricle-closing sound).
These sounds can be harnessed to give any number of medically relevant information. For instance, if one or more of the heart valves are not operating properly, the S1 or S2 sounds may be skewed, diminished, or not present. Since these sounds are easily identifiable using non-invasive procedures, it would be advantageous to develop systems that could take advantage of these sounds to develop medically relevant information.
It is often desirable to know a patient's respiratory rate, such as for a patient under anesthesia. If the respiratory rate falls dramatically, is erratic, or is non-existent, the patient may be suffering serious complications that need to be addressed. A system that can be used to measure respiration rate would be advantageous, especially if that system could rely on a non-invasive procedure such as monitoring heart sounds.
Monitoring physiological signals is generally done by measuring the amplitude of some variable, measuring the frequency at which some variable occurs, by measuring the time at which some variable occurs, or, more commonly, some combination of those factors. Not every physiological variable is susceptible to measurement by each of these techniques. When measuring variables by amplitude, noise can often be a problem. A patient who moves or has other monitoring equipment which introduces noise into the relevant monitor will often have amplitudes that vary erratically, or have noise effects that prevents fully accurate measurements from being made. These noise effects can sometimes be compensated, but often at the expense of the simplicity and sometimes the accuracy of the system. A system that does not need to rely on amplitude measurements to identify a physiologic data would be preferable.
Also, some patients may have multiple monitors and other medical devices connected to the patient at any one time. Some of these monitors and medical devices may use technologies or techniques that may interfere with the accuracy of other monitors or devices. It would be preferable to use a monitoring system that would not interfere with other monitors and devices. Also, it would be preferable to have a monitoring system that is generally not greatly affected by the presence of other monitors or medical devices.
While it is generally advantageous to measure respiration rate, many current respiration rate monitors tend to be cost-prohibitive for many patients. The amount of money available to be spent on the care of sub-acute patients (patients with less severe conditions) is generally less than that for patients with more severe conditions because monitoring of some sub-acute patients is typically considered more precautionary than critical. Thus, monitors that are relatively expensive or cumbersome are usually reserved for patients with conditions that are more severe. It would be desirable to have a respiration monitor that is less expensive. Additionally, it would be preferable to have a respiration monitor that is not very bulky.
Those patients who are monitored more heavily typically have a large number of separate machines connected to them at any one time. This increase in the number of machines increases the clutter associated with the heavily monitored patients. A system that could reduce the number of machines needed to monitor a patient would be advantageous.
The teachings hereinbelow extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.